I'm no expert on bomb sights and have trouble visualizing the description above, but I've seen the Estoppey D-8 sight be called a low-altitude bomb sight. I know nothing about the Sperry S-1, but that is another WW2 US bomb sight. The description above does not sound like the Mark Twain sight from the Doolittle Raid to me, there's mention of perspex and mirrors.
Also, the first paragraph says (at least to me) that this sight is not for retro-bombing, but currently used for practice bombing only. It could be some sort of training device instead.